Heat recovery apparatus

ABSTRACT

A heat recovery apparatus comprising a vessel having: a first liquid flow path such that a first liquid can pass through the vessel between a first liquid inlet and a first liquid outlet; a second liquid flow path in thermal contact with the first liquid flow path; and a heater for occasionally heating at least the liquid in the second liquid flow path on an occasional basis. This allows Legionella growth to be inhibited.

The present invention relates to a heat recovery apparatus, and inparticular to an apparatus suitable for recovering heat from “grey”water.

BACKGROUND OF THE INVENTION

Water after it has been used for washing or showing is often dischargeddirectly to the waste water, i.e. sewerage, systems. However such waterwhich is typically termed “grey” water may contain significant amountsof heat. For example most bathers get out of a bath while it is stillrelatively warm. Furthermore it is estimated that around 70 to 80% ofthe heat delivered into a shower leaves via the shower drain. Thus thereis significant potential to collect heat from such grey water.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided aheat recovery apparatus comprising a vessel having: a first liquid flowpath such that a first liquid can pass through the vessel between afirst liquid inlet and a first liquid outlet; a second liquid flow pathin thermal contact with the first liquid flow path; and a heater withinthe vessel for occasionally heating at least the liquid in the secondliquid flow path.

It is thus possible to provide a heat recovery apparatus which canrecover heat from grey water and deliver it to a further liquid such asa cold water supply. The cold water supply may be used as a cold waterinput to a boiler, thereby reducing the amount of work that needs to bedone by the boiler and hence the amount of fuel it consumes.Alternatively the water supply may go to items such as washing machinesand dishwashers thereby reducing their heating requirements.

However, having static volumes of previously warmed water can cause ahealth risk due to Legionella. It is therefore beneficial to provide aheater to occasionally heat at least the liquid in the second liquidflow path such that any Legionella in it is deactivated. The heater may,for example, be in the form of an electrical resistance heater embeddedwithin or formed in or on the second liquid flow path. However, it isgenerally more convenient to have the heater heat a volume of water thatis in contact with the second liquid flow path, thereby ensuring thatthat volume of water does not propose a Legionella risk either.

As an alternative to electrical heating, or in addition to electricalheating, a further pipe may be provided such that it can receive warmedwater from, for example, a primary circuit of a boiler such that waterwithin the heat recovery apparatus can be heated to at least 50° C., andpreferably 60° C. by the boiler.

The vessel may be configured such that it permanently retains a volumeof the grey water. Consequently the grey water can also act as a thermalstore thereby allowing more energy to be transferred to cold waterpassing through the second liquid flow path. As a variation, a dedicatedthermal store, for example in the form of a tank of water surroundingthe second liquid flow path may be provided, and the thermal store isitself in heat exchange contact with the grey water. Where a tank ofwater is provided as the thermal store the tank may be closed. Thisrepresents no explosion threat as the grey water passing through theheat recovery device will, by definition, be below the boiling point ofwater. Alternatively the tank may be open such that it vents toatmospheric pressure, or the pressure pertaining within the vessel ofthe heat recovery apparatus. When the tank is open it may be allowed torefill by being exposed to the grey water passing through the heatrecovery apparatus. This is a particularly safe arrangement as both thetank of water forming the thermal store and the grey water are openvented, such that even if a fault developed in the heater such that ittried to overheat the water in the heat recovery apparatus, the watercan boil away with no build up of pressure.

Advantageously a temperature operated valve, where the valve is eithermechanically or electrically controlled, may be provided in order toinhibit the grey water from being in substantial thermal exchange withthe second liquid flow path or the tank surrounding the second liquidflow path whilst the grey water is below a first threshold temperature.The first threshold temperature may be an absolute temperature, forexample 25° C., or it may be determined relative to the temperature ofthe water in the tank or in the second liquid flow path. This provides amechanism for preventing the passage of cold grey water through the heatrecovery apparatus from depleting the heat store of heat that it hadpreviously recovered and stored.

In an embodiment of the invention the boiler may be operated so as todeliberately heat the thermal store and/or grey water to store energy init such that the energy can be recovered at a later date.

Thus a pipe passing through the heat recovery apparatus may beselectively heated by the boiler, or may be selectively placed in acirculation path of water in a space heating circuit such that at, forexample heating shutdown, heat from the space heating circuit can berecovered and stored in the heat recovery apparatus. At a later event,such as at heating start up, water in the space heating circuit can flowthrough the pipe again to recover some heat, for re-use in the spaceheating circuit. The pipe can be the same pipe as provided for theoccasional heating of the store or could be a further pipe. Such anarrangement is disclosed in GB 2461077.

BRIEF DESCRIPTION OF THE FIGURES

The present invention will further be described, by way of non-limitingexample only, with reference to the accompanying Figures, in which:

FIG. 1 is a cross sectional diagram of a heat recovery apparatusconstituting a further embodiment of the present invention;

FIG. 2 is a cross sectional schematic diagram of a heat recoveryapparatus constituting a second embodiment of the present invention;

FIG. 3 is a cross sectional schematic diagram of a heat recoveryapparatus constituting a further embodiment of the present invention;and

FIG. 4 is a schematic diagram showing the connection of a heat recoveryapparatus constituting an embodiment of the present invention between acold water main and an appliance.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 schematically illustrates a first embodiment of the presentinvention which comprises a vessel, generally designated 2, having aninlet 4 arranged to receive grey water from a bath or shower and anoutlet 6 arranged to deliver grey water to a drain. The shape of thevessel is not particularly important, but it may advantageously berelatively long compared to its height or width such that it could beinstalled in the space beneath the bath, between floor joists, or undera kitchen cupboard. The vessel may be made of any suitable material,including metals or plastics. In use, the vessel fills with grey watersuch that this embodiment always contains a volume of grey water fromthe bath or shower. Thus the inlet pipe 4, the void in the interior ofthe vessel 2 and the outlet pipe 6 form a first liquid flow path.

In order to extract heat from the grey water a second liquid flow pathfor, for example, mains water, is provided by a pipe 10 which passesthrough the majority of the vessel 2. In order to improve the heattransfer characteristics the pipe may be provided with fins, but moreeasily is simply formed into a meandering path or a spiral or coil. Thepipe 10 can be placed in series connection between a water main and aboiler or some other domestic appliance such as a washing machine or adishwasher.

Because users, be they domestic or industrial, may not draw water forextended periods of time then there becomes a risk that Legionella,which occurs naturally, may multiply within the warmed region of thepipe 10 to such a level that they become a risk to health then meansneed to be provided in order to prevent this. It is known thatLegionella can be controlled by heating to above 50° C., and preferablyto above 60° C., so as to kill the bacteria. In order to achieve thisheating means, in this example in the form of an electrically poweredheater 12 is disposed within the heat recovery apparatus such that itcan be energised to heat the water in the pipe 10, and advantageouslyalso the grey water within the vessel 2 thereby preventing risk ofdisease. The heater 12 may be energised periodically by a time clock ora controller and may include an inline thermostat 14 to interrupt thepower supply to the heater 12 once the temperature of the water invessel 2 exceeds a predetermined upper limit, for example 65°, in orderto prevent excessive waste of energy or risk of boiling.

FIG. 2 shows a variation on the theme in FIG. 1 where a heat storagereservoir 20, in this instance in the form of a closed vessel 20 filledwith a suitable liquid, such as water, is provided within a vessel 22and the first liquid flow path from the inlet 4 to the outlet 6 is via achamber 24. An intermediate wall 26, which for example is formed ofmetal, provides a heat exchange boundary between grey water in thechamber 24 and a heat storage medium 28 in the reservoir or closedvessel 20. A cold water main 10 meanders through the reservoir 20 so asto pick up heat therefrom and a further pipe 30 allows heat from thewarmed fluid within the pipe 30 to heat the water 28 in the reservoir 20to above 50 or 60° C., and in so doing also warms the water within thepipe 10 to that temperature. The pipe 30 may, for example, be part of adedicated warming circuit or may be driven from the primary circuit of aboiler.

It can also be seen that heat exchange can occur across the wall 26 suchthat the grey water in the chamber 24 also gets heated. When the heatingis provided by the pipe 30 being filled with warmed liquid then there isno need to provide a thermostat within the reservoir 20 as the overheatcontrol systems of the boiler 30 control the temperature of the liquidin the pipe 30 in order to prevent boiling from occurring.

FIG. 3 shows a further variation which in many ways is similar to FIG. 2as a reservoir 20 containing water 28 is provided and the secondaryliquid flow path 10 meanders through the reservoir 20 so as to pick heatup from the water 28. However, as noted with respect to FIG. 2 in thatarrangement it is possible for heat exchange to occur from the reservoir20 to the grey water 24. The arrangement in FIG. 3 alleviates thisproblem because the inlet 4 and the outlet 6 are formed towards thebottom of the vessel 2 and, in addition, a restricted flow orifice, orseveral orifices are formed near the outlet 6 such that in the absenceof water inflow above a predetermined rate the grey water region 40 ofthe vessel 2 tends to drain. Furthermore, a thermostatically controlledvalve 42, for example in the form of a movable closure 44 co-operatingwith an orifice 46 may be provided such that if the water passingthrough the region 40 is too cold then it is ducted directly towards theoutlet 6 and is not allowed to collect in the region 40. This in turnprevents cold grey water from coming in contact with a heat exchangewall 26 of the reservoir 20. The temperature of the water could bedetermined by a mechanically operated temperature sensing valve, or asshown in FIG. 3 may be determined by an electronic temperature sensingelement 50 which is connected to a controller 52 which in turn controlsan electric actuator 54, such as a stepper motor or a solenoid which ismechanically connected to the valve 42 so as to open and close it.

Once the temperature detector 50 detects that the grey water issufficiently warm then the controller 52 actuates the actuator 54 so asto close the valve 42 thereby forcing the warm grey water to collectwithin the vessel 2 until such time as its level is sufficiently high toreach the top of an overflow pipe 56 which is in connection with thedrain 6. This arrangement ensures that any failure of the controller 52the temperature sensor 50 or the actuator 54 will not prevent thepassage of grey water towards a drain.

This arrangement not only has the advantage that cold water does notcome in contact with the reservoir 20, thereby depleting heat from itunnecessarily, but it also means that only the volume of water 28 in thereservoir 20 and in the section of the pipe 10 that passes through thereservoir 20 needs to be warmed by the heater in order to kill theLegionella bacteria. Further temperature sensors may be provided in thereservoir 20 in order to determine when it has been heated sufficiently,for example under the control of an electrical heater 60.

As mentioned before the heat exchange apparatus as shown in FIG. 1, 2 or3 may be placed in serious connection between the water main 70 and anappliance 72 as shown in FIG. 4. The appliance 72 might be a washingmachine or a dishwasher or alternatively could be a boiler for providingdomestic hot water.

It is thus possible to provide a heat recovery system for the recoveryof heat from grey water, but also to include means to prevent thebuild-up or growth of Legionella bacteria.

1. A heat recovery apparatus comprising a vessel having: a first liquidflow path such that a first liquid can pass through the vessel between afirst liquid inlet and a first liquid outlet; a second liquid flow pathin thermal contact with the first liquid flow path; and a heater withinthe vessel for occasionally heating at least the liquid in the secondliquid flow path.
 2. A heat recovery apparatus as claimed in claim 1, inwhich the first liquid is waste water from sinks, baths or showers.
 3. Aheat recovery apparatus as claimed in claim 1, in which the secondliquid flow path is in series with a cold water main.
 4. A heat recoveryapparatus as claimed in claim 1, in which the heater comprises anelectric heating element.
 5. A heat recovery apparatus as claimed inclaim 1, in which the heater comprises a third liquid flow path arrangedto be switched into communication with a boiler such that warmed liquidfrom the boiler is passed through the liquid flow path.
 6. A heatrecovery apparatus as claimed in claim 1, in which the vessel is adaptedto retain a predetermined volume of waste water therein.
 7. A heatrecovery apparatus as claimed in claim 1, in which the vessel has avalve or a flow restriction associated with the first outlet such thatin the absence of a flow of liquid into the first inlet the vessel tendsto empty.
 8. A heat recovery apparatus as claimed in claim 1, furthercomprising a heat store within the vessel associated with the secondliquid flow path.
 9. A heat recovery apparatus as claimed in claim 8, inwhich the heat store comprises a reservoir of liquid through which thesecond liquid flow path passes.
 10. A heat recovery apparatus as claimedin claim 9, in which the heat store is a closed container.
 11. A heatrecovery apparatus as claimed in claim 9, in which the heat store is anopen container.
 12. A heat recovery apparatus as claimed in claim 11, inwhich the heat store is replenished by the waste water.
 13. A heatrecovery apparatus as claimed in claim 8, in which the heat store islocated above the first liquid flow path.
 14. A heat recovery apparatusas claimed in claim 1 in combination with a boiler, wherein the heatrecovery apparatus is an inlet path to the boiler.
 15. A heat recoveryapparatus as claimed in claim 1 in which the heater is operated to heatat least the liquid in the second flow path to at least 50° C.